As generally known, an oil circulation lubrication is used for lubricating the gears at higher rotational speeds. For this type of lubrication, two conditions have been considered necessary:
(a) the oil hs to be able to flow freely from the gear chamber. PA1 (b) the outwardly guided spindle has to be sealed by labyrinth packings and centrifuge discs in such a way, that even when the spindle is at a standstill oil cannot reach the outside.
It is desirable to eliminate the spindle seal having contacting seals, as the spindle tends to heat up too much as a result of the rotation of the spindle.
With the above mentioned milling head pivotal around 90 degrees having horizontal and vertical working positions of the spindle, condition (a) cannot be fulfilled due to the mounting ratios, and as a result (b) also becomes ineffective, because the oil would run through the labyrinth packings during spindle standstill. At the moment a dosed grease lubrication is used predominantly.
This means that a dosed and sufficient lubrication is only possible within limits, so that the rotational speed of the spindle is limited. Additionally, with the state of the art, elaborate measures have to be taken for cooling the spindle and the bearings. Also, sufficient lubrication has to be provided for the drive gears in the spindle head carrier.
Additional lubrication problems arise for milling and drilling machines provided with a spindle head, which can bring the spindle into a horizontal or vertical working position with pivotal movement around 90 degrees, due to these pivotal movements and the different working positions resulting therefrom. This lubrication problem is therefore one of the main disadvantages of known machine tools, because these result in upper limits for the rotational speed of the spindle.